Antenna



Sept. 20, 1938. A. GOTHE 2,130,389

ANTENNA Filed June 5, 1936 & (fl META! L REFLECTOR l \IQ e P P M 4DIELECTRIC I REFLECTOR i 1" T DIELEC'fR/C L REFLECTOR INVENTOR ALBRECHTGOTHE vP gm ATTORN EY Patented Sept. 20, 1938 PATENT OFFICE ANTENNAAlbrecht Gothe, Berlin, Germany, assignor to Telefunken Gesellschaftfiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation ofGermany Application June 5, 1936, Serial No. 83,626 In Germany July 1,1935 3 Claims. (Cl. 250-41) The present invention relates to an antennareflector for short waves, more especially ultra short waves.

In many cases it is of advantage if unequivocally polarized waves can beradiated or received. Unequivocally polarized waves are sent out, forinstance, by a dipole radiator. However, in order to obtain a morefavorable exploitation of power, it will be of advantage to useconcentrated radiation. Concentration of electromagnetic waves isachieved by the combination of dipole radiators and reflectors. Thus,for instance, the known umbrella antennas consist of any desired numberof radiators arranged at a flat reflector whereby the reflector isformed of sheet metal or wire mesh.

Reflector arrangements act in various ways according to the polarizationof the waves impinging thereon. If, for instance, a wave arrives havinga polarization at right angles to the reflector surface, the reflectedwave has the same polarization as the impinging wave. If the impingingwave is polarized parallel to the reflector surface, the reflected wavehas the reversed polarization, 1. e., the polarization plane is thesame, but the phase of the wave is displaced by 180. When a wave isreflected whose polarization is inclined towards the reflector surface,a rotation is produced between the initial wave and the reflected wave,whereby the degree of rotation depends upon the relationship between thecomponent at right angle to the reflector and the component parallelthereto.

A better understanding of the invention may be had by referring to theaccompanying drawing, wherein:

Fig. 1 illustrates known practice, and

Figs. 2 and 3 illustrate two embodiments of the invention.

In Fig. l the radiating dipole D placed in front of the metallicreflector M is slightly inclined to the latter. The dipole sends outwaves with a polarization indicated by the arrows P. Owing to theinclination relative to the reflector plane the polarization of thewaves at reflection is slightly turned, the reflected wave thereforehaving a polarization as designated by the arrows R. Now, in addingboth, there will be obtained in place of a linearly polarized wave, awave having an elliptical polarization such as shown by the ellipse EL.Since in the practical structure of antennas difficulties areencountered in arranging the radiators exactly parallel to the reflectorplane, while on the other hand, absolutely flat reflector surfaces arediflicult to produce, it is hardly possible to produce unequivocallypolarized waves with linear polarization by means of the known antennareflector arrangements.

According to the invention, antenna arrangements for waves having linearpolarization are 1 obtained, making the reflectors for the antennas froma dielectric instead of from a conductor. It is known that at adielectric, reversal of polarization occurs for waves polarized parallelto the reflector plane as well as for those Whose polarization is atright angles to the reflector plane, i. e., the reflected wave has thesame direction of polarization as the incoming wave, but its phase isrotated by 180. Thus where a wave impinging on the dielectric reflectorhas its polarization turned relative to the reflector surface,

the reflected wave will still reveal the same polarization.

This case is illustrated in Fig. 2. The radiating dipole D is arrangedin front of the reflector T formed of a dielectric. As indicated in thedrawing the polarization P of the wave radiated by the dipole isparallel to the polarization R of the reflected wave.

Through suitable spacing between radiator and reflector, one can obtainthe sum of the direct and reflected wave despite the phase reversal atthe place of reflection.

Where a plurality of linear radiators such as two, for instance, are tobe arranged in front of the reflector surface and which are to functionindependently of each other, for example, one as a transmitting radiatorand the other as a receiving radiator, they Will ordinarily have to bedisposed crosswise at a right angle to each other. If the reflectorsurface consists of a material which is. a favorable electricalconductor such as metal, for instance, the crossed linear radiators mustnot have any inclination towards the reflector surface, since otherwiseowing to the rotative displacement of the polarization plane at thereflector an undesirable mutual coupling (radiation coupling) occurs.However, in a dielectric reflector it is possible to arrange the linearradiators, crossed at right angles to each other, at any angle towardsthe reflector surface,

Fig. 3 shows such arrangement of two crossed linear radiators D1 and D2in front of a dielectric reflector T. It is seen that the polarizationsplane of the direct wave (P1 and P2) and of the reflected wave (R1 andR2) form respectively a right angle with each other, so that no couplingexists between the radiators.

The front surface of dielectric does not reflect the entire radiationimpinging thereon but a portion passes through and is reflected at therear surface of the dielectric. This double reflection can be preventedsimply by forming the reflector of a material having a high absorptionproperty for electromagnetic waves, and which transforms the penetratingwaves into heat. The material may, for instance, also have the propertyof stepped up absorption. This method however, implies the loss of theenergy which enters into the material. This energy can, however, beutilized in avoiding absorption of the wave in the reflector, and by sochoosing the thickness of the reflector that the waves reflected at thefront and rear surface arrive in equal phase at the dipole radiator, sothat in this case the sum of the direct wave and of the two reflectedwaves will be obtained.

The invention, it is to be distinctly understood, is not limited to theembodiments herein shown and described.

What is claimed is:

1. In combination, a plane reflector consisting of a dielectric and anantenna in front of said reflector, said antenna comprising two linearradiators in substantially the same plane disposed at an angle of 90with respect to each other so as to form a cross, the plane of saidradiators being arranged at an angle between 0 and 90 with respect tothe plane of said reflector.

2. In combination, a plane reflector consisting of a dielectric and anantenna in front of said reflector, said antenna comprising two linearradiators in substantially the same plane disposed at an angle of 90with respect to each other so as to form a cross, the plane of saidradiators being arranged at an angle of 45 with respect to the plane ofsaid reflector.

3. In combination, an antenna and a reflector for said antenna, saidreflector being made of a dielectric material having a high coefficientof absorption and having front and back reflecting surfaces, thethickness of said material and absorption coeflicient thereof being sorelated that :l

the reflection from said back surface is prevented from adverselyaffecting the reflection from said front surface.

ALBRECHT GOTI-IE.

